MILLS, Wyo. (AP) — A Wyoming police officer has pleaded not guilty to an animal-cruelty charge that alleges a police dog died after he left it in a hot patrol car for several hours.

According to an investigator’s statement filed in Natrona County Circuit Court, Mills police officer Zachary Miller left the dog, a 10-year-old female black lab named Nyx, in his patrol car for over six hours July 9.

“It’s a tragedy,” Mills Mayor Marrolyce Wilson said.

The car was running, but the air conditioning was off and outside temperatures reached 86 degrees, KCWY News 13 reported (http://bit.ly/1tAzzhs).

Miller, a four-year veteran of the Mills Police Department, has pleaded not guilty to the misdemeanor charge, the Casper Star-Tribune reported Friday (http://bit.ly/1vsZr03 ).

KCWY reported that he appeared for a preliminary hearing Friday.

Nyx was trained to detect drugs and had been with the department since 2006. Miller had been her handler for the past two years, and the dog lived with his family and went on family vacations.

The affidavit states that Miller left the dog inside his car, went into the police department about 6 a.m. and did not return to the car until about 12:20 p.m. Police dogs are allowed inside the station, Preciado said.

During the time Miller was inside, he was training another officer on patrol-duty procedures. Miller is no longer a training officer, Preciado said. The officer who was with Miller that day will not be disciplined, Preciado said.

Miller remains employed by the police department but is currently not on active duty, Preciado said. He was suspended for a week with pay starting the day the dog died.

“It was a mistake he’s going to have to pay for,” Preciado said. “He’s going to be disciplined through our department.”

Miller had never faced disciplinary action by the department before this incident, Preciado said. He was named “Officer of the Year” in 2013.

The dog had assisted Casper Police, Wyoming Highway Patrol, the Division of Criminal Investigation and the Natrona County Sheriff’s Office, Preciado said. A plaque or other kind of memorial will be created in the dog’s memory at the police department, he said.

The dog’s body was buried on Miller’s property, Preciado said. “Everyone was hurt by her loss,” he said.

Nyx was the department’s first and only police dog. The department has suspended its K9 program and is reviewing its policies, Preciado said.

Alarms will be installed in the K9 patrol car before the department acquires a new police dog, Preciado said. The alarm will come with a key fob that dog handlers will carry that will alert them when the car gets too hot or too cold.